A system has been ordinary used as a system for forming a radiograph for medical diagnosis, in which a silver halide photographic light-sensitive material is contacted with an intensifying screen, and imagewise exposed to X-ray, and developed, fixed and washed by an automatic processor. It has been known in such the system that a sharpness of image is considerably lowered by diffusion of light at the time of exposing the light-sensitive material to light-image converted from X-ray image by the intensifying screen.
On the other hand, recently a system becomes to be used, in which a stimulus phosphor plate is imagewise exposed to X-ray and the stimulus phosphor plate is scanned by a laser light beam to readout the image information accumulated in the stimulus phosphor, as a light signal, the light signal is converted to an electric signal and reconverted to a light signal, and the light signal is recorded on a silver halide photographic light-sensitive material by scanning, and the light-sensitive material is developed, fixed, washed and dried by an automatic processor.
Such the system has an advantage such as that an image processing such as gradation controlling, edge stressing and masking can be applied since the image signal is once converted to the electric signal capable of being electrically processed, compared to the phosphor intensifying screen/film system. However, the sharpness of the image is insufficient for a mammographic image or radiographic image of bones of limbs.
It is theoretically expected that a high sharpness can be obtained by the method by directly reading out the image signal from the flat panel detector difficultly reproduced by an usual laser recording system. A system using a laser thermal diffusion transfer process has been also known as the laser recording system other than that using a silver halide photographic light-sensitive material. In the thermal transfer method, an image receiving sheet and a thermally fusible colorant sheet are superposed and an image is thermally transferred. Such the method has problems such as that the sharpness is insufficient, the apparatus is expensive and the image formation speed is low.